Process of manufacturing aminoguanidine



Patented Mar. 10, 1936 STATES PATENT or es PROCESS OF MANUFACTURINGAMINOGUANIDINE No Drawing. Application May 3, 1932,

Serial No. 609,043

13 Claims.

dine by reducing nitroguanidine by means of zinc.

dust and. acetic acid. (Thiele Ann. 270, 20 (1898) 302, 333 (1898)). Insuch a method a large excess of zinc dust is used and for the reasonthat only 50% yields are obtainable this method has been regarded asunsatisfactory. Aminoguanidine has also been prepared from hydrazine andmethylisothiourea but this method is also unsatisfactory because of theexpensive reagents that are used.

An object of this invention is an improved process of making substitutedand unsubstituted aminoguanidines. A further object is to improvegenerally upon the manufacture of substituted and unsubstitutedguanidines. Other objects will appear hereinafter, as the descriptionproceeds.

According to this invention these aminoguanidines can be produced verysatisfactorily by the catalytic reduction of nitroguanidines. Althoughin the following discussion nitroguanidine is described in detail, theinvention is applicable to substituted nitroguanidines in general, e. g.ditolylnitroguanidine, unsymmetrical diphenylnitroguanidine,xylylnitroguanidine, naphthylnitroguanidine, ethylnitroguanidine,butylnitroguanidine, triphenylnitroguanidine and like compounds.

According to this invention the reduction should be carried out withhydrogen in the presence of a catalyst at a relatively low temperature.It is advantageous to operate the process at temperatures such that theaminoguanidine will not be pyrolytically decomposed. It has been foundalso that if the hydrogenation is carried too far decomposition of theaminoguanidine results with consequent formation of urea and ammonia.

For the purpose of this invention a nickel catalyst and hydrogen arepreferred for the reduction of the nitroguanidine. Other hydrogenatingcatalysts may, however, be used, for example metallic catalysts preparedin a finely divided condition. Suitable catalysts may be selected fromthe group of metals known as the hydrogenating metals, comprising theelements copper, nickel, iron and cobalt and the noble metals of the 8thgroup of the periodic table such as platinum and palladium, rhodium, oralloys of two or more of these metals. In this process it has been founddesirable to keep the temperature as low as possible to preventdecomposition, e. g., below 125 C. Temperatures between 25 C. and 85 C.are satisfactory and preferably the temperatures should be between and85 C. Also it is preferred to operate the process at such pressures aswill permit the hydrogenation to proceed at a rate in excess of the rateof decomposition of the products. Suitable results may be obtained at ahydrogen pressure above 400 lbs. per sq. in. Lower pressures lead toincomplete conversion and the excessive formation of by-products. Good.results have been obtained when operating the process at a pressure ofabout 1100 lbs. per sq. in., although higher pressures even as high as3000 lbs. /-sq. in. may be used in some cases. For the reason that acidsand bases catalyze the decomposition of aminoguanidine it has been foundthat this may be "overcome by the addition of a buffering matriaLsuch asmagnesium sulfate, mixtures of alkaline phosphates, or mixtures of boraxwith boric acid and sodium chloride, which serves to reduce'thedecomposition. While carbondioxide neutralizes the aminoguanidine it issufficiently acid in reaction to decompose it.

The following examples are given as specific embodiments which furtherillustrate my invention:

Example 1 A hydrogenation catalyst is prepared by suspending kieselguhrin a solution of nickel nitrate. Basic nickel carbonate is precipitatedon the kieselguhr by adding sodium carbonate solution. The mass ofkieselguhr and basic nickel carbonate is washed several times bydecantation and filtered. The catalyst is then activated by reducing thebasic nickel carbonate by means of hydrogen.

Ten and four tenths grams of nitroguanidine, 5 grams of the abovecatalyst, and 200 grams of water are placed in a steel reaction vesselcapable of being heated. The reaction vessel is sealed, attached to asource of hydrogen, and heated to C. with good agitation under ahydrogen pressure of 1200 lbs. per sq. in. until the calculated amountof hydrogen has been absorbed. The reaction vessel is then unloaded. Theaminoguanidine is recovered by filtering off the catalyst, evaporatingthe neutralized solution and precipitating the aminoguanidine as amino--guanidine bicarbonate by addition of sodium bicarbonate.

Example 2 Ten and four tenths grams of nitroguanidine and 5 grams of thecatalyst described in Example 1 are suspended in 200 grams of watersolution containing 7 grams of magnesium sulfate. The mixture is placedin a steel reaction vessel capable of being heated. The reaction vesselis sealed, attached to a supply of hydrogen, and heated to C. with goodagitation under a hydrogen pressure of 800 lbs/sq. in. After thecalculated amount of hydrogen has been absorbed, the reaction vessel isunloaded and the aminoguanidine isolated as described in Example 1.

Example 3 Ten and four tenths grams of nitroguanidine and 5 grams of thecatalyst described in Example 1 are suspended in 200 grams of ethylacetate. The mixture is placed in a steel reaction vessel capable ofbeing heated. The reaction vessel is sealed, attached to a supply ofhydrogen,

and heated to 80 C. with good agitation under a hydrogen pressure of 800lbs/sq. in. After the calculated amount of hydrogen has been absorbed,the reaction vessel is unloaded and'the aminoguanidine isolated asdescribed in Example 1.

The resulting aminoguanidine may be isolated by filtration andneutralizing with dilute sulfuric acid. To the solution, afterevaporation, is added potassium bicarbonate to precipitate theaminoguanidine. The solution may then be cooled, filtered, and theproduct dried.

The statements inserted in the claims in the substantial absence ofacids" and in the absence of any substantial amount of acids are used todefine the invention yet not limiting it as to the presence of smallamounts of acidinadvertently present as impurities in thenitroguanidine. The presence of some acid would be expected, at least insome instances, since the nitroguanidine used is separated from asolution high in sulphuric acid.

I claim:

l. The process of producing an aminoguanidine which comprises thereduction of nitroguanidine with hydrogen at a temperature between 25 C.and 125 C. in the presence of a hydrogenation metal catalyst, and in theabsenceof any substantial amount of acids.

2. The process of claim 1, in which the metal catalyst is a nickelcatalyst.

3. The process of claim 1, in which the metal catalyst is taken from agroup consisting 01' copper, nickel, iron, and cobalt. 5

4. The process of claim 1, in which the catalyst is taken from theeighth group of the periodic table.

5. The process of producing aminoguanidine which comprises the reductionof unsubstituted 10 nitroguanidine with hydrogen at a temperaturebetween 25 C. and 125 C. in the presence of a hydrogenation metalcatalyst and in the absence of any substantial amount of acids.

6. The process of producing aminoguanidine 15 which comprises reducingnitroguanidine by means of hydrogen in the presence of a hydrogenationmetal catalyst and in the absence of any substantial amount of acids,operating the process at a pressure above 400 pounds per square 20 inch,and maintaining the temperature of the reaction between 25 C. and 125 C.

7 The process of claim 6, in which the pressure is maintained between400 pounds and 1200 pounds per square inch. 25

8. The process of claim 6, in which the pressure is maintained between400 pounds and 3000 pounds per square inch.

' 9. The process of producing an aminoguanidine which comprises reducingnitroguanidine by 30 means of hydrogen in the presence of ahydrogenation metal catalyst, and in the absence of any substantialamount of acids, operating the process in the presence of a bufferingmaterial and at a pressure above 400 pounds per square inch.

10. The process of claim 9, in which the bufferingmaterial is analkaline material.

11. The process of claim 9, in which the buffering material is magnesiumsulfate. -30

12. The process of claim 9, in which the buffering material is a mixtureof phosphates of the alkali metals.

13. The process of claim 9, in which the buffering material is a mixtureof borax with boric acid 45,

and sodium chloride.

RUSSELL McGILL;

